Radio locating arrangements



NOV 25, 1947 P. K. CHATTERJEA ETAL 2,431,305

RADIO LOCATING ARRANGEMENTS Filed June 24. 1943 l/aL TJV FREaz/E/yc Y H64. By ,7,

m l l Attney Patented Nov. 25, 1947 RADIO LOCATIN G ARRANGEMENTS Prafulla Kumar Chatterjea and Leslie Wilfred England, assignors to Standard Telephones and Cables Limited, London, England, a British company Application June 24, 1943, Serial No. 492,080 In Great Britain July 17, 1942 Houghton,

8 Claims.

The present invention relates to radio locating arrangements and has for its object to provide arrangements for giving indications for directing two or more mobile units, hereinafter called Chaser units, towards another mobile unit, hereinafter called a chased unit. The chased unit may be, for instance, an enemy vessel at sea, or an enemy aircraft sought by an allied vessel or aircraft. Each of the Chaser units is provided with radio means for determining the distance between said chaser unit and the chased unit in terms of a frequency. Such means are now well known in the art and in particular means utilising the known frequency sweep method or electric pulse method may be used since such means give directly a frequency representative of the distance between the chaser unit and the chased unit.

In arrangements utilising the frequency sweep method of distance determination, a carrier frequency is transmitted and is cyclically frequencymodulated over a frequency range or sweep at a number of Cycles per second. The waves after reection from the chased unit are received and heterodyned with the contemporaneously transmitted waves in order to obtain the difference frequency. This difference frequency is representative of the distance between the transmitter and the chased unit. In the pulse arrangement the repetition frequency of the pulses is adjusted until a transmitted and received pulse coincide. In this type of circuit the pulses will have to be repeated at slower frequencies as the distance increases, in order to make a transmitted and a received pulse coincide. It is considered that no further description of these arrangements is necessary herein.

According to one aspect of the present invention arrangements for indicating the relative positions of two or more mobile Chaser units `with respect to a mobile chased unit, each chaser unit being provided with radio means for determining the distance between said Chaser unit and the chased unit in terms of frequency, are characterised in this that each chaser unit is also provided with means for transmitting said frequency to the other Chaser units, with means for determining the difference frequency between the frequency representing its own distance from the chased unit and the frequency received from one of the other chaser units, and with means for utilising said difference frequency to obtain an indication as to which direction the chaser unit should proceed London,

(Cl. Z50-1.7 0)

in so that said difference frequency will be reduced toward zero.

According to another aspect of the invention arrangements for indicating the direction to two or more mobile chaser units towards a mobile chased unit, each chaser unit being provided with radio means for determining the distance between said chaser unit and chased unit in terms of a frequency, is characterised in this, that at least two of said chaser units are provided with means for transmitting said frequency to the other chaser units, and each Chaser unit is provided with means for determining the difference frequencies between the frequency representing its own distance from said chased unit and the said transmitted frequencies from at least two of the chaser units and with means for utilising said difference frequencies to obtain automatically an indication as to in which direction the chaser unit should proceed so that said difference frequencies will be reduced toward zero.

It will be realised that the arrangements may be continuously operating, in which case a continuous indication for directing of the chaser aircraft towards the chased aircraft would be obtained, or the arrangements may work intermittently.

The invention will be better understood from the following description taken in conjunction with the accompanying drawings in which:

Fig. 1 is an explanatory diagram;

Fig. 2 shows diagrammatically arrangements for obtaining an indication on the chaser units of the direction in which the unit should proceed so that the difference between the frequencies representing the distances of two chaser aircraft from the chased aircraft will be reduced towards zero; and

Fig. 3 is a characteristic curve of the filters used in the arrangements shown in Fig. 2.

Fig. 4 is a block diagram illustrating a complete system embodying the invention.

Referring to the drawings consider the case of two mobile locators A and B (Fig. 1) for example, two ghter aircraft which are able to determine the distance away of the located object O (Fig. l) in terms of a frequency. If OA is longer than OB when the frequency indication of locator A say fr. will be lower than that of locator Bs indication say fs. It is necessary for automatic action that either A or B or both be able to convert these two relative frequencies into a quantity, such as a voltage, which is capable of giving complete information of required directional changes that should take place in order to cause fA and fB to become equal, irrespective of their actual Values. A circuit arrangement capable of performing this function is shown in Fig. 2 where I and 2 are two identical lterswhich have characteristicsas shown in FigfS and to which the frequencies Vfri and -jB are respectively fed. The outputs from l and 2 are rectied by two diodes 5 and 6 to which they are fed via transformers 3 and 4. The D. O. outputs from both rectiers areobt`ained smoothed out in series oppositiongacross resistance-condenser networks f 'l-andY 8 andi-the difference voltage is fed -to,theig 1id,;'0f3l i/alYe amplifier 9, the required output then b;eing;.obtained between terminals mand. Il.

Suppose JA be fed to terminals 'l2 ande l3,- and fB to terminals i4 and i5 after having been corrected if necessary to the samek amplitude, then depending upontheir Value of frequency, the 1 output amplitudes from the filters I` andi 2 will be modified. If JA is the-higher; frequency ,-itkv will-have the,v` higher; output `amplitude when Y applied to,- rectier 5, .than Yfis which -isnsimul- .taneously applied to rectifierdfso thatia rela- .Y tivelylarger D.gC.voltage will bedeveloped across 1f andV 8, vthus altering, the total series voltage across them, 4rand hence the bias of valve 9 s0 ,-.alterinsz the;` output voltagesubetween; terminals 'This Vvoltage variationisgthen employedto obtainanindication Vonxa,Voltiileter for example. The voltage above or b1elow `that ob etait-led ,forno difference of potential between ,the

ends of resistances 'l` or- 8Y will give an;indica`. .x tion of: the direction.` the .Y aircraft should; .take '.Ltowards the'ohased'aircraft. ,Y For example, the 4aircraft B v at thegreatersdistance fromiO. will -be Vcausedvto veer' round ,towardsglO until thevoltageidifference between the remotelends ,of net=L works l andv .B carriedby the` aircraftrB is zero.

When the frequency difference is reversed in sign;,the aircraft A wilLbe further'V awayrf-rom O and JBfwill begreatemthanfrA and:the1vo1tage acrossnetworkg 3 of the equipmentqcarriedrby B Willlbe greater than; the Voltage :acrossl network l .of thesame equipment. fBLut thereversecwill be the case on aircraft A and henceaircraft `A will be directed to veer-round towards'O. :Thus the aircraft -A .and Barefsteered alternately,

until,` theyl have; closedi n; ,upo n theA chased` aircraft O.

Fig.` 4 shows therchased -unit at Orand on each side thereof `the apparatuswhich maybe carried A,bythe chaser units Aand B to enable; themto v. close, in` on the vchased units. `This-apparatus vatA includes asweep transmitter, a: re-

ceiver, and heterodyne Acircuit connected .to lter l whereby a frequency Fais Suppliedtto Athe -differential circuit, a receiver-connected toz'filter 2 for receivingfa,frequency-Fxfromnthe regular -transiriitter of the VChaser `unit a regular transmitter for transmitting the' frequencyfl-TA kto the chaserunitB, Aandan indicator-connected 1,to the output ,of the diierential. circuitsupplied :Item filters i. and 2. :The details. of-y the differential circuitiare, shown in,E.-ig.:,2.

rSimilar,apparatus is shownLlocated on Chaser punit` B. VThe regular transmitterat B. Willtransimita frequencygiFB tov the'receiver` and;;iilter:2 .l

onchasergunit A.

The transmitters fro m A andgBg-radiatega g beamed transmission ahead and z-k these beams shouldgbe fairlybroad with-agwide areazof over- .ilip- 30` vantageously placed above the bomber.

4 The carrier'frequencies used by the aircraft would of course, have to be different for the two aircraft A and B, and each would have a receiver capable of picking up the transmission from the 5 other directly, for communicating the respective A,distances from the chasedaircraft O.

An-indication would, of course, :be given to the fighter pilots A and B of the actual distance ,-away of the chased aircraft, for example, a bomber, O, Vso Ythat when within striking range they-Would be Yready for one to attack direct or ,..readyfor thebomber O, if it swung sharply to the Vvlv.right-for.leftso crossing in front of A or B.

fInvisibility-.mrc so bad that the fighters could ;'notlsee eachother, known radio methods would haveto be used for keeping the correct relative ,-positionsbetween the aircraft A and B.

Whilst the arrangements according to the ypresentinvention have been described assuming the chaser units located in a horizontal plane, .fit-.twill be clear Vto those skilled inthe art that a similarfarrangementmay beusedby two chaser .funitsin a vertical plane so that a further Chaser cunitrGcould' co-operatewitheither or both units -1-A'andB to close in on the chased unit O ingia vyerticaldirection as well-as theY horizontal direction. This yarrangement in space hasthe 4advantage that on contact being. made wthathe .-bomber, one'at least ofthe fighters-will be ad- It will 1 bev understood that each chaser unit will transv,.rnitits, distance frequency; on its respectivewaye 1 lengthyorrelse the chasers wheni thereareseveralv couldv transmit y only during respective'rsuccessive periods.

Whilst va voltmeter orV similar instrument-'has been ir1dicated'- asbeing suitable for` the in dicating instrumenton-thechaser 'unitfit will be understood that; otherfindicating devices` such Lipas,olialiarnpsmeans for producinga note of the difference frequency orother similar ,devices may-be employed and their adaptation tothe Apresent..invention will, be4 clearto those skilled in theart.

.lhatise4 claimed is: -1..-,ArrangementsY for; indicating the yrelative u positions-of a :plurality of mobile chaser units n.with respect to amobile chased unit, each Chaser lunitbeing provided wit-hgradio means for` dei terminingf ftheildistance between said chaserfunit :andy the-chased unit inl terms of a, frequency, A characterised inthis that feach chasersunit Yis alsqprovideclwith `lrneans for; transmitting VSaid Yfrequency Vto the other 4chaser units with means sfordeterminingthe diiferencebetween the frequency representing its own distance from the chasedunit and theA frequency received from one of the, other chaser-unitsand with means for V4,utilising saidqiiference to obtainan indication forthedirection in which the Chaser-unit should .proceedso :that saidedifferencewill be reduced toward( zero.

"2. Arrangements as claimedin claim 1 char- -acterised in this` that said means vfor determining gsaid Hdifference frequency comprises lmeans forderivingwdirectecurrent `voltages whose values `areedepemient'-upon said frequencies, said Voltages being-applied in-opposition to Van indicat- `ving instrument. i

3..iArrangemen-ts-ets-claimed in claim 1 characterised 1inY this that the frequency received :ifroin onepf the other chaser .units and the fre- -iquency representativel of 'the .distance of the schaser...unit.=,are. passedathrough respective filters 475L-having similar linear.:characteristicsof voltage tance of said chased unit from a rst of said Chaser units, means for determining the distance of said chased unit from a second of said Chaser units, means to deliver to said first Chaser unit a signal in the form of a Voltage Corresponding nto the algebraic diierence betweensaid distances, whereby an indication is provided of the direction in which said first Chaser unit must go to reduce said diierence to zero, and means to deliver a signal to said second Chaser unit signifying a value corresponding to the algebraic difference of said distances, whereby an indication is provided in said second Chaser unit of the direction in which said second Chaser unit is to go to reduce said difference to zero.

5. A system in accordance with Claim 4, in which the means to determine the distance from the chased unit of a Chaser unit is located in the particular Chaser unit.

6. A system in accordance with Claim 4, in which each means to determine the distance between the chased unit and a Chaser unit is 1o- Cated in said Chaser unit and means to deliver the diierence between the distances to each of said Chaser units includes means in each Chaser unit to transmit information Corresponding to the distance of said Chaser unit from said chased unit.

7. The method of guiding a plurality of mobile Chaser units for Closing in on a chased mobile unit which comprises determining the distance of one Chaser unit from said chased unit, determining the distance of another Chaser unit from said chased unit, taking the algebraic difference of said distances, and producing an indication of direction in each of said Chaser units determined by said difference.

8. The method of guiding a pair of mobile Chaser units so as to Close in on a mobile chased unit which comprises obtainingrin each of saidKVV REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Name Date Crosby Jan. 6, 1942 Guanella Jan. 6, 1942 Number 

